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Abstract:

New compositions and methods of using those compositions as bonding
compositions are provided. The compositions comprise a cycloolefin
copolymer dispersed or dissolved in a solvent system, and can be used to
bond an active wafer to a carrier wafer or substrate to assist in
protecting the active wafer and its active sites during subsequent
processing and handling. The compositions form bonding layers that are
chemically and thermally resistant, but that can also be softened or
dissolved to allow the wafers to slide or be pulled apart at the
appropriate stage in the fabrication process.

Claims:

1. A composition useful for bonding two substrates together, said
composition comprising a cycloolefin copolymer and an ingredient
dissolved or dispersed in a solvent system, said ingredient being
selected from the group consisting of tackifier resins, low molecular
weight cycloolefin copolymers, and mixtures thereof.

2. The composition of claim 1, said composition comprising from about 5%
to about 85% by weight of said copolymer, based upon the total weight of
the composition taken as 100% by weight.

4. The composition of claim 1, said copolymer being formed from the
polymerization of a cyclic olefin selected from the group consisting of
##STR00008## and combinations of the foregoing, where: each R1 and
R2 is individually selected from the group consisting of --H, and
alkyl groups; and each R3 is individually selected from the group
consisting of --H, substituted and unsubstituted aryl groups, alkyl
groups, cycloalkyl groups, aralkyl groups, ester groups, ether groups,
acetyl groups, alcohols, aldehyde groups, ketones, nitriles, and
combinations thereof.

5. The composition of claim 4, wherein said cyclic olefin is polymerized
with an acyclic olefin selected from the group consisting of branched and
unbranched C2-C20 alkenes.

6. The composition of claim 1, wherein said copolymer comprises recurring
monomers of: ##STR00009## and combinations of the foregoing, where:
each R1 and R2 is individually selected from the group
consisting of --H, and alkyl groups; and each R3 is individually
selected from the group consisting of --H, substituted and unsubstituted
aryl groups, alkyl groups, cycloalkyl groups, aralkyl groups, ester
groups, ether groups, acetyl groups, alcohols, aldehyde groups, ketones,
nitriles, and combinations thereof; and ##STR00010## where: - - - is a
single or double-bond; and each R4 is individually selected from the
group consisting of --H and alkyl groups.

7. The composition of claim 1, where said ingredient is present in said
composition at a level of from about 2% to about 80% by weight, based
upon the total weight of the composition taken as 100% by weight.

9. The composition of claim 1, wherein said ingredient is a low molecular
weight cycloolefin copolymer having a weight average molecular weight of
less than about 50,000 Daltons.

10. The composition of claim 1, wherein said composition is essentially
free of adhesion promoting agents.

11. The composition of claim 1, said composition having thermal stability
up to a temperature of about 350.degree. C.

12. The composition of claim 1, said composition being essentially free
of crosslinking agents.

13. The composition of claim 1, said composition further comprising an
antioxidant selected from the group consisting of phenolic antioxidants,
phosphite antioxidants, phosphonite antioxidants, and mixtures thereof.

14. The composition of claim 1, said composition having a melt viscosity
of less than about 100 PaS at the debonding temperature of said
composition.

[0004] The present invention is broadly concerned with novel compositions
and methods of using those compositions to form bonding compositions that
can support active wafers on a carrier wafer or substrate during wafer
thinning and other processing.

[0007] Geometrical limitations are an additional incentive for substrate
thinning. Via holes are etched on the backside of a substrate to
facilitate frontside contacts. In order to construct a via using common
dry-etch techniques, geometric restrictions apply. For substrate
thicknesses of less than 100 μm, a via having a diameter of 30-70
μm is constructed using dry-etch methods that produce minimal
post-etch residue within an acceptable time. For thick substrates, vias
with larger diameters are needed. This requires longer dry-etch times and
produces larger quantities of post-etch residue, thus significantly
reducing throughput. Larger vias also require larger quantities of
metallization, which is more costly. Therefore, for backside processing,
thin substrates can be processed more quickly and at lower cost.

[0008] Thin substrates are also more easily cut and scribed into ICs.
Thinner substrates have a smaller amount of material to penetrate and cut
and therefore require less effort. No matter what method (sawing, scribe
and break, or laser ablation) is used, ICs are easier to cut from thinner
substrates. Most semiconductor wafers are thinned after frontside
operations. For ease of handling, wafers are processed (i.e., frontside
devices) at their normal full-size thicknesses, e.g., 600-700 μm. Once
completed, they are thinned to thicknesses of 100-150 μm. In some
cases (e.g., when hybrid substrates such as gallium arsenide (GaAs) are
used for high-power devices) thicknesses may be taken down to 25 μm.

[0009] Mechanical substrate thinning is performed by bringing the wafer
surface into contact with a hard and flat rotating horizontal platter
that contains a liquid slurry. The slurry may contain abrasive media
along with chemical etchants such as ammonia, fluoride, or combinations
thereof. The abrasive provides "gross" substrate removal, i.e., thinning,
while the etchant chemistry facilitates "polishing" at the submicron
level. The wafer is maintained in contact with the media until an amount
of substrate has been removed to achieve a targeted thickness.

[0010] For a wafer thickness of 300 μm or greater, the wafer is held in
place with tooling that utilizes a vacuum chuck or some means of
mechanical attachment. When wafer thickness is reduced to less than 300
μm, it becomes difficult or impossible to maintain control with regard
to attachment and handling of the wafer during further thinning and
processing. In some cases, mechanical devices may be made to attach and
hold onto thinned wafers, however, they are subject to many problems,
especially when processes may vary. For this reason, the wafers ("active"
wafers) are mounted onto a separate rigid (carrier) substrate or wafer.
This substrate becomes the holding platform for further thinning and
post-thinning processing. Carrier substrates are composed of materials
such as sapphire, quartz, certain glasses, and silicon, and usually
exhibit a thickness of 1000 μm. Substrate choice will depend on how
closely matched the coefficient of thermal expansion (CTE) is between
each material. However, most of the currently available adhesion methods
do not have adequate thermal or mechanical stability to withstand the
high temperatures encountered in backside processing steps, such as
metallization or dielectric deposition and annealing. Many current
methods also have poor planarity (which contributes excessive total
thickness variation across the wafer dimensions), and poor chemical
resistance.

[0011] One method that has been used to mount an active wafer to a carrier
substrate is via a thermal release adhesive tape. This process has two
major shortcomings. First, the tapes have limited thickness uniformity
across the active wafer/carrier substrate interface, and this limited
uniformity is often inadequate for ultra-thin wafer handling. Second, the
thermal release adhesive softens at such low temperatures that the bonded
wafer/carrier substrate stack cannot withstand many typical wafer
processing steps that are carried out at higher temperatures.

[0012] Thermally stable adhesives, on the other hand, often require
excessively high bonding pressures or bonding temperatures to achieve
sufficient melt flow for good bond formation to occur. Likewise, too much
mechanical force may be needed to separate the active wafer and carrier
wafer because the adhesive viscosity remains too high at practical
debonding temperatures. Thermally stable adhesives can also be difficult
to remove without leaving residues.

[0013] There is a need for new compositions and methods of adhering an
active wafer to a carrier substrate that can endure high processing
temperatures and that allow for ready separation of the wafer and
substrate at the appropriate stage of the process.

SUMMARY OF THE INVENTION

[0014] The present invention overcomes the problems of the prior art by
broadly providing a wafer bonding method, which includes providing a
stack comprising first and second substrates bonded together via a
bonding layer, and separating the first and second substrates. The
bonding layer is formed from a composition comprising a cycloolefin
copolymer (COC) dissolved or dispersed in a solvent system.

[0015] The invention also provides an article comprising first and second
substrates and a bonding layer. The first substrate comprises a back
surface and an active surface, which comprises at least one active site
and a plurality of topographical features. The second substrate has a
bonding surface. The bonding layer is bonded to the active surface of the
first substrate and to the bonding surface of the second substrate. The
bonding layer is formed from a composition comprising a cycloolefin
copolymer dissolved or dispersed in a solvent system.

[0016] In a further embodiment, the invention is concerned with a
composition useful for bonding two substrates together. The inventive
composition comprises a cycloolefin copolymer and an ingredient dissolved
or dispersed in a solvent system. The ingredient is selected from the
group consisting of tackifier resins, low molecular weight cycloolefin
copolymers, and mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 illustrates the inventive method of thinning and debonding
two wafers according to the present invention;

[0018] FIG. 2 is a flow diagram showing the typical process steps followed
in the examples;

[0019] FIG. 3 is a graph depicting the rheological analysis results of
bonding compositions according to the invention debonded at 150°
C.;

[0020] FIG. 4 is a graph depicting the rheological analysis results for
bonding compositions according to the invention debonded at 200°
C.; and

[0021] FIG. 5 is a graph depicting the rheological analysis results for
bonding compositions according to the invention debonded at 250°
C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In more detail, the inventive compositions comprise a cycloolefin
copolymer (COC) dispersed or dissolved in a solvent system. The copolymer
is preferably present in the composition at levels of from about 5% to
about 85% by weight, more preferably from about 5% to about 60% by
weight, and most preferably from about 10% to about 40% by weight, based
upon the total weight of the composition taken as 100% by weight.

[0023] The preferred copolymers are thermoplastic and preferably have a
weight average molecular weight (M) of from about 2,000 Daltons to about
200,000 Daltons, and more preferably from about 5,000 Daltons to about
100,000 Daltons. Preferred copolymers preferably have a softening
temperature (melt viscosity at 3,000 PaS) of at least about 100°
C., more preferably at least about 140° C., and even more
preferably from about 160° C. to about 220° C. Suitable
copolymers also preferably have a glass transition temperature (Tg)
of at least about 60° C., more preferably from about 60° C.
to about 200° C., and most preferably from about 75° C. to
about 160° C.

[0025] Preferred acyclic olefins are selected from the group consisting of
branched and unbranched C2-C20 alkenes (preferably
C2-C10 alkenes). More preferably, suitable acyclic olefins for
use in the present invention have the structure

##STR00002##

where each R4 is individually selected from the group consisting of
--H and alkyl groups (preferably C1-C20 alkyls, more preferably
C1-C10 alkyls). Particularly preferred acyclic olefins for use
in the present invention include those selected from the group consisting
of ethene, propene, and butene, with ethene being the most preferred.

[0026] Methods of producing cycloolefin copolymers are known in the art.
For example, cycloolefin copolymers can be produced by chain
polymerization of a cyclic monomer with an acyclic monomer (such as
norbornene with ethene as shown below).

##STR00003##

The reaction shown above results in an ethene-norbornene copolymer
containing alternating norbornanediyl and ethylene units. Examples of
copolymers produced by this method include TOPAS®, produced by
Goodfellow Corporation and TOPAS Advanced Polymers, and APEL®,
produced by Mitsui Chemicals. A suitable method for making these
copolymers is disclosed in U.S. Pat. No. 6,008,298, incorporated by
reference herein.

[0027] Cycloolefin copolymers can also be produced by ring-opening
metathesis polymerization of various cyclic monomers followed by
hydrogenation as illustrated below.

##STR00004##

The polymers resulting from this type of polymerization can be thought of
conceptually as a copolymer of ethene and a cyclic olefin monomer (such
as alternating units of ethylene and cyclopentane-1,3-diyl as shown
below).

##STR00005##

Examples of copolymers produced by this method include ZEONOR® from
Zeon Chemicals, and ARTON® from JSR Corporation. A suitable method of
making these copolymers is disclosed in U.S. Pat. No. 5,191,026,
incorporated by reference herein. Accordingly, copolymers of the present
invention preferably comprise recurring monomers of:

[0030] where: [0031] is a single or double-bond; and [0032] each
R4 is individually selected from the group consisting of --H and
alkyl groups (preferably C1-C20 alkyls, more preferably
C1-C10 alkyls).

[0033] The ratio of monomer (I) to monomer (II) within the polymer is
preferably from about 5:95 to about 95:5, and more preferably from about
30:70 to about 70:30.

[0034] The inventive compositions are formed by simply mixing the
cycloolefin copolymer and any other ingredients with the solvent system,
preferably at room temperature to about 150° C., for time periods
of from about 1-72 hours.

[0035] The composition should comprise at least about 15% by weight
solvent system, preferably from about 30% to about 95% by weight solvent
system, more preferably from about 40% to about 90% by weight solvent
system, and even more preferably from about 60% to about 90% by weight
solvent system, based upon the total weight of the composition taken as
100% by weight. The solvent system should have a boiling point of from
about 50-280° C., and preferably from about 120-250° C.
Suitable solvents include, but are not limited to, methyl ethyl ketone
(MEK) and cyclopentanone, as well as hydrocarbon solvents selected from
the group consisting of limonene, mesitylene, dipentene, pinene,
bicyclohexyl, cyclododecene, 1-tert-butyl-3,5-dimethylbenzene,
butylcyclohexane, cyclooctane, cycloheptane, cyclohexane,
methylcyclohexane, and mixtures thereof.

[0036] The total solids level in the composition should be at least about
5% by weight, preferably from about 5% to about 85% by weight, more
preferably from about 5% to about 60% by weight, and even more preferably
from about 10% to about 40% by weight, based upon the total weight of the
composition taken as 100% by weight.

[0037] According to the invention, the composition can include additional
ingredients, including low molecular weight cycloolefin copolymer (COC)
resins and/or tackifier resins or rosins. The composition can also
include a number of optional ingredients selected from the group
consisting of plasticizers, antioxidants, and mixtures thereof.

[0038] When a low molecular weight COC resin is used in the composition,
it is preferably present in the composition at a level of from about 2%
to about 80% by weight, more preferably from about 5% to about 50% by
weight, and even more preferably from about 15% to about 35% by weight,
based upon the total weight of the composition taken as 100% by weight.
The term "low molecular weight cycloolefin copolymer" is intended to
refer to COCs having a weight average molecular weight (Mw) of less
than about 50,000 Daltons, preferably less than about 20,000 Daltons, and
more preferably from about 500 to about 10,000 Daltons. Such copolymers
also preferably have a Tg of from about 50° C. to about
120° C., more preferably from about 60° C. to about
90° C., and most preferably from about 60° C. to about
70° C. Exemplary low molecular weight COC resins for use in the
present compositions are those sold under the name TOPAS® Toner TM
(Mw 8,000), available from Topas Advanced Polymers.

[0039] When a tackifier or rosin is utilized, it is preferably present in
the composition at a level of from about 2% to about 80% by weight, more
preferably from about 5% to about 50% by weight, and even more preferably
from about 15% to about 35% by weight, based upon the total weight of the
composition taken as 100% by weight. The tackifiers are chosen from those
having compatible chemistry with the cycloolefin copolymers so that no
phase separation occurs in the compositions. Examples of suitable
tackifiers include, but are not limited to, polyterpene resins (sold
under the name SYLVARES® TR resin; Arizona Chemical), beta-polyterpene
resins (sold under the name SYLVARES® TR-B resin; Arizona Chemical),
styrenated terpene resins (sold under the name ZONATAC NG resin; Arizona
Chemical), polymerized rosin resins (sold under the name SYLVAROS® PR
resin; Arizona Chemical), rosin ester resins (sold under the name
EASTOTAC® resin; Eastman Chemical), cyclo-aliphatic hydrocarbon resins
(sold under the name PLASTOLYN® resin; Eastman Chemical, or under the
name ARKON® resin; Arakawa Chemical), C5 aliphatic hydrocarbon resins
(sold under the name PICCOTAC® resin; Eastman Chemical), hydrogenated
hydrocarbon resins (sold under the name REGALITE® resin; Eastman
Chemical), and mixtures thereof.

[0040] When an antioxidant is utilized, it is preferably present in the
composition at a level of from about 0.1% to about 2% by weight, and more
preferably from about 0.5% to about 1.5% by weight, based upon the total
weight of the composition taken as 100% by weight. Examples of suitable
antioxidants include those selected from the group consisting ofphenolic
antioxidants (such as pentaerythritol
tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate sold under the
name IRGANOX® 1010 by Ciba), phosphite antioxidants (such as
tris(2,4-ditert-butylphenyl)phosphite sold under the name IRGAFOS®
168 by Ciba), phosphonite antioxidants (such as
tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diylbisphosphonite
sold under the name IRGAFOX® P-EPQ by Ciba), and mixtures thereof.

[0041] In alternative embodiments, it is preferred that the compositions
are essentially free (less than about 0.1% and preferably about 0% by
weight) of adhesion promoting agents, such as
bis(trimethoxysilylethyl)benzene, aminopropyl tri(alkoxy silanes) (e.g.,
aminopropyl tri(methoxy silane), aminopropyl tri(ethoxy silanes), -phenyl
aminopropyl tri(ethoxy silane)), and other silane coupling agents, or
mixtures thereof. In some embodiments, the final composition is also
thermoplastic (i.e., noncrosslinkable). Thus, in these alternative
embodiments, the composition will be essentially free (less than about
0.1% by weight and preferably about 0% by weight) of crosslinking agents,
such as POWDERLINK® by Cytec, and EPI-CURE® 3200 by Hexion
Specialty Chemicals.

[0042] According to one aspect, the melt viscosity (complex coefficient of
viscosity) of the final composition will preferably be less than about
100 PaS, more preferably less than about 50 PaS, and even more preferably
from about 1 PaS to about 35 PaS. For purposes of these measurements, the
melt viscosity is determined via rheological dynamic analysis (TA
Instruments, AR-2000, two parallel-plate configuration where the plates
have a diameter of 25 mm). Furthermore, the melt viscosity is preferably
determined at the preferred debonding temperature of the composition in
question. As used herein, the term "preferred debonding temperature" of
the composition is defined as the temperature at which the melt viscosity
of the composition is below 100 PaS, and is determined by dynamic
measurement at 1 Hz oscillation frequency in temperature ramp. The
compositions also preferably have a storage modulus (G') of less than
about 100 Pa, preferably less than about 50 Pa, and even more preferably
from about 1 Pa to about 26 Pa, when measured at the preferred debonding
temperature of the composition. The storage modulus is determined by
dynamic measurement at 1 Hz oscillation frequency in temperature ramp.

[0043] The compositions are thermally stable up to about 350° C.
There is also preferably less than about 5% by weight, and more
preferably less than about 1.5% by weight, loss of the composition after
one hour at the preferred debonding temperature plus 50° C.
(preferably at a temperature of from about 200° C. to about
300° C.), depending upon the composition. In other words, very
little to no thermal decomposition occurs in the composition at this
temperature, as determined by thermogravimetric analysis (TGA), described
herein.

[0044] Although the composition could be applied to either the carrier
substrate or active wafer first, it is preferred that it be applied to
the active wafer first. These compositions can be coated to obtain
void-free thick films required for bump wafer applications and to achieve
the required uniformity across the wafer. A preferred application method
involves spin-coating the composition at spin speeds of from about
500-5000 rpm (more preferably from about 1000-3500 rpm), at accelerations
of from about 3000-10,000 rpm/second, and for spin times of from about
30-180 seconds. It will be appreciated that the application steps can be
varied to achieve a particular thickness.

[0045] After coating, the substrate can be baked (e.g., on a hot plate) to
evaporate the solvents. Typical baking would be at temperatures of from
about 70-250° C., and preferably from about 80-240° C. for
a time period of from about 1-60 minutes, and more preferably from about
2-10 minutes. The film thickness (on top of the topography) after bake
will typically be at least about 1 μm, and more preferably from about
10-200 μm.

[0046] After baking, the desired carrier wafer is contacted with, and
pressed against, the layer of inventive composition. The carrier wafer is
bonded to this inventive composition by heating at a temperature of from
about 100-300° C., and preferably from about 120-180° C.
This heating is preferably carried out under vacuum and for a time period
of from about 1-10 minutes, under a bond force of from about 0.1 to about
25 kiloNewtons. The bonded wafer can be subjected to backgrinding,
metallization, patterning, passivation, via forming, and/or other
processing steps involved in wafer thinning, as explained in more detail
below.

[0047] FIG. 1(a) illustrates an exemplary stack 10 comprising active wafer
12 and carrier wafer or substrate 14. It will be appreciated that stack
10 is not shown to scale and has been exaggerated for the purposes of
this illustration. Active wafer 12 has an active surface 18. As shown in
FIG. 1(a), active surface 18 can comprise various topographical features
20a-20d. Typical active wafers 12 can include any microelectronic
substrate. Examples of some possible active wafers 12 include those
selected from the group consisting of microelectromechanical system
(MEMS) devices, display devices, flexible substrates (e.g., cured epoxy
substrates, roll-up substrates that can be used to form maps), compound
semiconductors, low k dielectric layers, dielectric layers (e.g., silicon
oxide, silicon nitride), ion implant layers, and substrates comprising
silicon, aluminum, tungsten, tungsten silicide, gallium arsenide,
germanium, tantalum, tantalum nitrite, SiGe, and mixtures of the
foregoing.

[0048] Carrier substrate 14 has a bonding surface 22. Typical carrier
substrates 14 comprise a material selected from the group consisting of
sapphire, ceramic, glass, quartz, aluminum, silver, silicon,
glass-ceramic composites (such as products sold under the name
Zerodur®, available from Schott AG), and combinations thereof.

[0049] Wafer 12 and carrier substrate 14 are bonded together via bonding
composition layer 24. Bonding layer 24 is formed of the cycloolefin
copolymer compositions described above, and has been applied and dried as
also described above. As shown in the FIG. 1(a), bonding layer 24 is
bonded to active surface 18 of wafer 12 as well as to bonding surface 22
of substrate 14. Unlike prior art tapes, bonding layer 24 is a uniform
(chemically the same) material across its thickness. In other words, the
entire bonding layer 24 is formed of the same composition.

[0050] It will be appreciated that, because bonding layer 24 can be
applied to active surface 18 by spin-coating or spray-coating, the
bonding composition flows into and over the various topographical
features. Furthermore, the bonding layer 24 forms a uniform layer over
the topography of active surface 18. To illustrate this point, FIG. 1
shows a plane designated by dashed line 26, at end portion 21 and
substantially parallel to back surface 16. The distance from this plane
to bonding surface 22 is represented by the thickness "T." The thickness
"T" will vary by less than about 20%, preferably by less than about 10%,
more preferably by less than about 5%, even more preferably by less than
about 2%, and most preferably less than about 1% across the length of
plane 26 and substrate 14.

[0051] The wafer package can then be subjected to subsequent thinning (or
other processing) of the substrate as shown in FIG. 1(b), where 12'
presents the wafer 12 after thinning. It will be appreciated that the
substrates can be thinned to thicknesses of less than about 100 μm,
preferably less than about 50 μm, and more preferably less than about
25 μm. After thinning, typical backside processing, including
backgrinding, patterning (e.g., photolithography, via etching),
passivation, and metallization, and combinations thereof, may be
performed.

[0052] Advantageously, the dried layers of the inventive compositions
possess a number of highly desirable properties. For example, the layers
will exhibit low outgassing for vacuum etch processes. That is, if a
15-μm thick film of the composition is baked at 80-250° C. for
2-60 minutes (more preferably 2-4 minutes), the solvents will be driven
from the composition so that subsequent baking at 140-300° C. for
2-4 minutes results in a film thickness change of less than about 5%,
preferably less than about 2%, and even more preferably less than about
1.0% or even 0% (referred to as the "Film Shrinkage Test"). Thus, the
dried layers can be heated to temperatures of up to about 350° C.,
preferably up to about 320° C., more preferably up to about
300° C., without chemical reactions occurring in the layer. In
some embodiments, the layers can also be exposed to polar solvents (e.g.,
N-methyl-2-pyrrolidone) at a temperature of 80° C. for 15 minutes
without reacting.

[0053] The bond integrity of the dried layers can be maintained even upon
exposure to an acid or base. That is, a dried layer of the composition
having a thickness of about 15 μm can be submerged in an acidic media
(e.g., concentrated sulfuric acid) or base (e.g., 30 wt. % KOH) at
85° C. for about 45 minutes while maintaining bond integrity. Bond
integrity can be evaluated by using a glass carrier substrate and
visually observing the bonding composition layer through the glass
carrier substrate to check for bubbles, voids, etc. Also, bond integrity
is maintained if the active wafer and carrier substrate cannot be
separated by hand.

[0054] After the desired processing has occurred, the active wafer or
substrate can be separated from the carrier substrate. In one embodiment,
the active wafer and substrate are separated by heating to a temperature
sufficient to soften the bonding layer. More specifically, the stack is
heated to temperatures of at least about 100° C., preferably at
least about 120° C., and more preferably from about 150° C.
to about 300° C. These temperature ranges represent the preferred
debonding temperatures of the bonding composition layer. This heating
will cause the bonding composition layer to soften and form softened
bonding composition layer 24' as shown in FIG. 1(c), at which point the
two substrates can be separated, for example, by sliding apart. FIG. 1(c)
shows an axis 28, which passes through both of wafer 12 and substrate 14,
and the sliding forces would be applied in a direction generally
transverse to axis 28. Instead of sliding, wafer 12 or substrate 14 can
be separated by lifting upward (i.e., in a direction that is generally
away from the other of wafer 12 or substrate 14) to separate the wafer 12
from the substrate 14.

[0055] Alternatively, instead of heating to soften the layer, the bonding
composition can be dissolved using a solvent. Once the layer is
dissolved, the active wafer and substrate can be thereafter separated.
Suitable solvents for use in dissolving the bonding layer can be any
solvent that was part of the composition prior to drying, such as those
selected from the group consisting of MEK and cyclopentanone, as well as
hydrocarbon solvents selected from the group consisting of limonene,
mesitylene, dipentene, pinene, bicyclohexyl, cyclododecene,
1-tert-butyl-3,5-dimethylbenzene, butylcyclohexane, cyclooctane,
cycloheptane, cyclohexane, methylcyclohexane, and mixtures thereof.

[0056] Whether the bonding composition is softened or dissolved, it will
be appreciated that separation can be accomplished by simply applying
force to slide and/or lift one of wafer 12 or substrate 14 while
maintaining the other in a substantially stationary position so as to
resist the sliding or lifting force (e.g., by applying simultaneous
opposing sliding or lifting forces to wafer 12 and substrate 14). This
can all be accomplished via conventional equipment.

[0057] Any bonding composition remaining in the device areas can be easily
removed by rinsing with a suitable solvent followed by spin-drying.
Suitable solvents include the original solvent that was part of the
composition prior to drying as well as those solvents listed above
suitable for dissolving the composition during debonding. Any composition
remaining behind will be completely dissolved (at least about 98%,
preferably at least about 99%, and more preferably about 100%) after 5-15
minutes of exposure to the solvent. It is also acceptable to remove any
remaining bonding composition using a plasma etch, either alone or in
combination with a solvent removal process. After this step, a clean,
bonding composition-free wafer 12' and carrier substrate 14 (not shown in
their clean state) will remain.

EXAMPLES

[0058] The following examples set forth preferred methods in accordance
with the invention. It is to be understood, however, that these examples
are provided by way of illustration and nothing therein should be taken
as a limitation upon the overall scope of the invention.

Example 1

Cycloolefin Copolymer Resin and Low Molecular Weight COC Resin Blends

[0059] In this Example, formulations containing cycloolefin copolymers and
a low molecular weight COC resin were made. Antioxidants were added to
some of the formulations.

[0060] 1. Sample 1.1

[0061] In this procedure, 1.2 grams of an ethene-norbornene copolymer
(TOPAS® 5010, Tg 110° C.; obtained from TOPAS Advanced
Polymers, Florence, Ky.) were dissolved in 6 grams of D-limonene (Florida
Chemical Co.), along with 2.8 grams of a low molecular weight cycloolefin
copolymer (TOPAS® Toner TM, Mw 8,000, Mw/Mn 2.0). The
solution was allowed to stir at room temperature until the ingredients
were in solution. The solution had about 40% solids.

[0062] 2. Sample 1.2

[0063] In this procedure, 0.75 grams of an ethene-norbornene copolymer
(TOPAS® 8007, Tg 78° C.) and 3.25 grams of low molecular
weight COC (TOPAS® Toner TM) were dissolved in 6 grams of D-limonene.
The solution was allowed to stir at room temperature until the
ingredients were in solution. The solution had about 40% solids.

[0064] 3. Sample 1.3

[0065] For this procedure, 1.519 grams of an ethene-norbornene copolymer
(TOPAS® 5013, Tg 134° C.) were dissolved in 5.92 grams of
D-limonene along with 2.481 grams of a low molecular weight cycloolefin
copolymer (TOPAS® Toner TM), 0.04 grams of a phenolic antioxidant
(IRGANOX® 1010), and 0.04 grams of a phosphonite antioxidant
(IRGAFOX® P-EPQ). The solution was allowed to stir at room
temperature until the ingredients were in solution. The solution had
about 40% solids.

[0066] 4. Sample 1.4

[0067] In this procedure, 1.2 grams of an ethene-norbornene copolymer
(TOPAS® 8007) were dissolved in 5.92 grams of D-limonene along with
2.8 grams of a low molecular weight cycloolefin copolymer (TOPAS®
Toner TM), 0.04 grams of a phenolic antioxidant (IRGANOX® 1010), and
0.04 grams of a phosphonite antioxidant (IRGAFOX® P-EPQ). The
solution was allowed to stir at room temperature until the ingredients
were in solution. The solution had about 40% solids.

[0068] 5. Sample 1.5

[0069] For this procedure, 2.365 grams of an ethene-norbornene copolymer
(TOPAS® 5013) were dissolved in 5.92 grams of D-limonene along with
1.635 grams of a low molecular weight cycloolefin copolymer (TOPAS®
Toner TM), 0.04 grams of a phenolic antioxidant (IRGANOX® 1010), and
0.04 grams of a phosphonite antioxidant (IRGAFOX® P-EPQ). The
solution was allowed to stir at room temperature until the ingredients
were in solution. The solution had about 40% solids.

[0070] 6. Sample 1.6

[0071] In this procedure, 2.2 grams of a hydrogenated norbornene-based
copolymer prepared by ring-opening polymerization (ZEONOR® 1060,
Tg 100° C.; obtained from Zeon Chemicals, Louisville, Ky.)
and 1.8 grams of a low molecular weight cycloolefin copolymer (TOPAS®
Toner TM) were dissolved in 5.92 grams of cyclooctane (Aldrich,
Milwaukee, Wis.). The solution was allowed to stir at room temperature
until the ingredients were in solution. The solution had about 40%
solids.

Example 2

Cycloolefin Copolymer Resins and Tackifier Blends

[0072] In this Example, formulations were made containing cycloolefin
copolymers blended with various tackifiers. As in Example 1, antioxidants
were added to some of the formulations.

[0073] 1. Sample 2.1

[0074] In this procedure, 0.83 grams of an ethene-norbornene copolymer
(TOPAS® 8007) were dissolved in 5.92 grams of D-limonene, along with
3.17 grams of a hydrogenated hydrocarbon resin (REGALITE® R1125;
obtained from Eastman Chemical Co., Kingsport Tenn.), 0.04 grams of a
phenolic antioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite
antioxidant (IRGAFOX® P-EPQ). The solution was allowed to stir at
room temperature until the ingredients were in solution. The solution had
about 40% solids.

[0075] 2. Sample 2.2

[0076] For this procedure, 0.7 grams of an ethene-norbornene copolymer
(TOPAS® 8007) and 3.3 grams of a styrenated terpene resin
(ZONATAC® NG98; obtained from Arizona Chemical, Jacksonville, Fla.)
were dissolved in 5.92 grams of D-limonene, along with 0.04 grams of a
phenolic antioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite
antioxidant (IRGAFOX® P-EPQ). The solution was allowed to stir at
room temperature until the ingredients were in solution. The solution had
about 40% solids.

[0077] 3. Sample 2.3

[0078] In this formulation, 1.9 grams of an ethene-norbornene copolymer
(TOPAS® 5013) were dissolved in 5.92 grams of D-limonene, along with
2.1 grams of a cyclo-aliphatic hydrocarbon resin (ARKON® P-140;
obtained from Arakawa Chemical USA Inc., Chicago, Ill.), 0.04 grams of a
phenolic antioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite
antioxidant (IRGAFOX® P-EPQ). The solution was allowed to stir at
room temperature until the ingredients were in solution.

[0079] 4. Sample 2.4

[0080] For this procedure, 2.42 grams of an ethene-norbornene copolymer
(TOPAS® 5013) were dissolved in 5.92 grams of D-limonene, along with
1.58 grams of a cyclo-aliphatic hydrocarbon resin (PLASTOLYN® R-1140;
obtained from Arakawa Chemical USA Inc., Chicago, Ill.), 0.04 grams of a
phenolic antioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite
antioxidant (IRGAFOX® P-EPQ). The solution was allowed to stir at
room temperature until the ingredients were in solution. The solution had
about 40% solids.

Example 3

Application, Bonding and Debonding, and Analysis

[0081] The formulations prepared in Examples 1 and 2 above were
spin-coated onto various substrate wafers. After baking to evaporate the
solvent and allowing the bonding composition to reflow, a second wafer
was bonded to each coated wafer by applying pressure. A typical procedure
for temporary wafer bonding using the bonding compositions is illustrated
in FIG. 2. The bonded wafers were tested for mechanical strength, thermal
stability, and chemical resistance. The wafers were tested for debonding
by manually sliding them apart at acceptable temperatures. After
debonding, the bonding composition residue was cleaned using a solvent
rinse and spinning.

[0082] The rheological properties of each formulation from Examples 1 and
2 were tested. All of these materials were successfully tested for
debonding. It was determined that the preferred debonding temperature for
samples 1.1, 1.2, 2.1, and 2.2 was 150° C. The preferred debonding
temperature for samples 1.3, 1.4, and 2.3 was 200° C., and the
preferred debonding temperature for samples 1.5, 1.6, and 2.4 was
250° C. The storage modulus (G') and melt viscosity (η*,
complex coefficient of viscosity) for each sample at their preferred
debonding temperatures are reported below. The rheological data is also
illustrated in FIGS. 3-5 for each debonding temperature.

[0083] Further studies on thermal stability and chemical resistance were
also carried out on these compositions. Thermogravimetric analysis (TGA)
was carried out on a TA Instruments thermogravimetric analyzer. The TGA
samples were obtained by scraping off the spin-coated and baked bonding
composition samples from Examples 1 and 2. For the isothermal TGA
measurement, the samples were heated in nitrogen at a rate of 10°
C./min., up to their preferred debonding temperature plus 50° C.,
and kept constant at that temperature for 1 hour to determine the thermal
stability of the particular bonding composition. The isothermal
measurements for each sample formulation are reported below in Table 2.
For the scanning TGA measurement, the samples were heated in nitrogen at
a rate of 10° C./min. from room temperature to 650° C.

[0084] As can be seen from the Table above, all of the COC-low molecular
weight COC resin blends (Example 1) possessed the required thermal
stability at least up to 300° C. and exhibited minimal weight loss
(<1.5-wt %). The COC-tackifier blends (Example 2) had an average
weight loss of about 5-wt % when maintained at the testing temperature.
However, as shown in Table 3, below, the 1-wt % weight loss temperatures
were higher than their respective bonding/debonding temperatures,
suggesting sufficient thermal resistance for wafer-bonding applications.

[0085] To determine chemical resistance, two silicon wafers were bonded
using the particular bonding composition to be tested. The bonded wafers
were put into chemical baths of N-Methyl-2-Pyrrolidone (NMP) or 30% by
weight KOH at 85° C., and concentrated sulfuric acid at room
temperature to determine chemical resistance. The bond integrity was
visually observed after 45 minutes, and the stability of the bonding
composition against the respective chemical was determined. All bonding
compositions retained the bond integrity.

Patent applications by Dongshun Bai, Rolla, MO US

Patent applications by Rama Puligadda, Rolla, MO US

Patent applications by Tony D. Flaim, St. James, MO US

Patent applications by Wenbin Hong, Rolla, MO US

Patent applications by BREWER SCIENCE INC.

Patent applications in class Phosphorus bonded to only two chalcogen atoms and having at least one P-C linkage

Patent applications in all subclasses Phosphorus bonded to only two chalcogen atoms and having at least one P-C linkage